Method and apparatus for sheathing a structural member with a synthetic thermoplastic material



R. COLOMBO May 7, 1963 3,088,166

METHOD AND APPARATUS RoR SHEATHINC A STRUCTURAL MEMBER WITH A SYNTHETIC THERMOPLASTIC MATERIAL Filed oct. I5, 1959 Fig. 2

Fig. 7

United States Patent O 3,(l8,166 METHOD AND APPARATUS FR SHEA'IHING A SIRUCIURAL MEMBER WITH A SYNTHETIC THERMGPLASTIS MATERIAL Roberto Colombo, Turin, Italy, assigner to SAS. Lavorazione Materie Plastiche (LME.) di M.. I. Colombo @e C., Turin, Italy Filed Get. 13, 195% Ser. No. 846,262 Claims priority, application Italy Get. 2t), 1953 Ciaims. (Cl. it-13) This invention relates to sheathing of mostly metallic structural members with a synthetic thermoplastic material by simultaneously advancing the structural member through an extrusion head for the material and extruding on the said structural member la protective layer of the material, such -as polyvinyl chloride, polyethylene and other thermoplastic materials.

Sheathing by the above method of the structural members having .a convex outer prole, such as tubes and bars of circular, square, polygonal, etc. cross-sectional shape does not generally meet Iwith particular diiliculties and almost 'always leads to a composite article in which the sheath satisfactorily adheres to lthe structural member. Only when using linear superpolyamides ditiiculties were met in assuring adherence, the said diiiculties having `been obviated by applying vacuum at the inlet of the Structural member into the extrusion head, whereby the sheathing materid was sucked against the structural member during extrusion.

The use of metallic structural members in the manufacture of frames for doors, windows and glass walls generally, considerably expanded `of late, and attempts were made at sheathing the said structural members with protective layers of synthetic plastic material, such as polyvinyl chloride. However, the said structural members have their cross-sectional shape of a concave proiile, [that is, comprising one concave angle at least, and it was found that at the -said concave angle the layer of synthetic plastic material never adhered to the structural member but suffered a distortion such as to considerably alter the original profile of the structural member, as will be better explained hereinafter.

The primary object of this invention is therefore to provide a method Iand means adapted to cause the sheath of synthetic thermoplastic material to adhere to the structural member even at the concave angles in the latter, independently of the type of thermoplastic material employed for the sheathing.

All the characteristic features and .advantages of this invention will be understood from the appended description referring to the accompanying drawing .given by way of example only, wherein:

FIGURES 1 and 2 are cross-sectional views of two structural members sheathed with a synthetic thermoplastic material, showing the drawbacks mentioned above;

FIGURE 3 shows diagrammatically the -apparatus `according to this invention;

FIGURE 4- is a cross-sectional view on line IV-IV of FIGURE 3 on an enlarged scale and `FIGURE. 5 is a par-t sectional perspective View ott a sheathed structural member as the sheathing is setting.

In FIGURE l a metallic structural member d@ of Z- shaped proiile is shown, which is sheathed with a layer 11 of thermoplastic material. The sheathing has been made according to conventional abovementioned techniques, by advancing the structural member coaxially through an extrusion head and extruding thereon the synthetic plastic material in a softened condition through `an extrusion nozzle similar in cross-sectional shape to that ofy the structural member. At the inlet for the structural member into the head a device known .per se was fitted in dhd Patented May 7, 1963 "ice order to tightly insulate the portion of the structural member conned in the head and apply thereto a certain degree of vacuum. Nevertheless, as shown by FIGURE l, the sheathing material 11 became loosened from the structural member 10 Aat the concave angles 12, 1.2', thereby altering in a lfully incontrolled manner the original aspect of the cross-section of the structural member. Considering that a structural member of this kind should be associated with other members in a struct-ure of predetermined size, it will be understood lthat a sheathed structural member of this kind is not usable.

Conditions are still worst inthe case shown in FIGURE 2, in which the sheath 14 of synthetic plastic material has drawn appreciably apart from the structural member 113 along the three faces rforming together the concave angles 15, l5'.

It should be noted that FIGURES 1 and 2 are merely diagrammatical and :of an illustrative character, distortions actually arising in the practice being much more complex and of an vextent not to be foreseen or controlled by means heretofore available.

In FIGURE 3, 20 denotes an extrusion head of a structure known per se fed with softened synthetic thermoplastie material from a screw press (not sho-wn) through a connection 21. The head is formed with an axial passage through which a structural member 22 to be sheathed can be advanced in a downward direction. This structural member 22 is of L-shape, as will be seen more clearly in FIGURES 4 .and 5, `and the extrusion nozzle 23 on the head 29 comprises ya die of a similar L- shaped profile in order to deposit on the structural member a sheathing layer 24 which should accurately match the configuration of the cross-section of the structural member 22. Reference 25, FIGURE 3, denotes a sealing device, known per se, fitted to the head 20 at its inlet end for the structural member 22, connected with a source of vacuum generally indicated on the drawing by a pump 26.

According to this invention as soon as the sheathed lower end portion of the structural member 22 issues downwardly from the head 20, the layer of thermoplastic material sheathing this end portion is tightly pressed against the structural member, for instance in the manner shown in FIGURE 4. In this figure a spongy rubber block 27 of quadrant form is forced Iby its apex against the hollow angle in the prole 4and secured in these conditions by means of a rubber band 28. yIn this manner a restricted length of a few centimeters of the sheath -24 is clamped in a fluid-tight manner throughout the contour of the cross-sectional area of the structural member 2,2, thereby preventing access of outer -air between the sheath of the structural member from the -fore end of the latter. The extrusion head and the pump 26 are then again operated, the structural member y2.2. being simultaneously advanced through lthe head and sheathed with the thermoplastic material. The sheathed length i221' of the structural member issuing from the head is cooled in a manner known per se, such as by means of water jets.

It has been -found that the above measures are thoroughly sutlicient .to cause the sheath to satisfactorily adhere to the structural member, provided the material of the sheath is relatively soft, such as polyethylene, and provided also .the thickness of the sheath is small as compared with the width A tof the wings of the structural member. However, the requirement in the technical ield is mostly for a relatively hard sheathing, mostly of polyvinyl chloride with a considerable proportion -of fillers, so that further features of this invention should then be resorted to, as described hereinafter.

Assuming the structural member 22, FIGURE 3, should be sheathed with rigid polyvinyl chloride, the same course is followed as above by first sheathing the fore end of the prole to make it .accessible beneath the head 20, ywhereafter vacuum is lapplied to this end also. For this purpose 4a hollow needle 3i) (FIG. 5) is axially -tted yat the concave angle in the structural member between the latter and the sheath, .the needle 30 having a head 31 for connection through .a -hose 32 with .a source of vacuum indicated in FIGURE 3 by a pump 33. 'I'his end of the structural member is then clamped by means of the rubber band 2S and the spongy rub-ber block 27, as previously described with reference to FIGURE 4, care being taken yof limiting the .clamping region to a length located within the length of the needle, thereby leaving free and unobstructed the free end of the latter. Thus, the length of the needle should be in any case greater Ithan Vthe length of the -associated rubber block 27. At this stage the sheathing proper is carried out by operating the head 29 Iand pumps .26, 33, and simultaneously advancing the structural member 22 through the head. As the sheathed portion 22 of the .structural member issues downwardly from .the head 20, it is cooled by means orf water jets as mentioned above, whereby the sheath 24 sets and is stabilized starting from the leading (lower) end of the structural member. By this procedure the -tail end (which is the upper end on the drawing) of the structural member 22 linally appears beneath the head 26, the said end .being sheathed with still softened material 24, but being no longer submitted to vacuum from means 25, y25. The risk now .arises that the sheathing 24 may become loosened from the concave angle on the structural member throughtout the length over which the sheathing material has not yet set. In order to obviate this risk the sheath 24 is tightly pressed at the tail end of the structural member also .against the latter (FIGURE such as by means of a spongy rubber block 37 land a rubber band 3S similarly as described with reference to FIGURE 4. The structural member is then merely subjected to vacuum `set up through the needle 30 Iand is `further cooled in these conditions till full setting .of 4the shea-th, whereupon the needle 30 yis withdrawn yand the clamping means 27, 28 and 37, 38 removed.

.By cutting a structural member sheathed as above to pieces, it will be seen that the sheathing is uniform and no loosening between the sheath l241and structural member 22 is visible `to the eye, so that the sheathed member is .of a desired cross-'sectional coniiguration and size. Only a magnifying glass will disclose the existence between .the sheath y24 and structural member 22 of merely capillary passages, which exactly .act in propagating vacuum Afrom the needle 30 throughout the length of the structural member to the clamping means 37, 38, thereby holding the sheath 24 sucked against the structural member 22 till se-tting.

As mentioned above, or carrying out the above process vacuum set up by the means 2.5 and 2,6 is broken at the end of lthe process. In some particular cases this might result in part loosening of the sheath by an extent such as it cannot be subsequently annulled by the mere action of the needle 30 after iitting the clamping means 37, 38 to the tail end of the structural member. According to a modification of the process described above it might be convenient in such cases to stop extrusion 'and arrest the structural member .2.2 shortly before its tail end disappears within the head 20. By this procedure the means 25, 26 associated with the tail end `of the structural member will be further operative, while the clamping means 37, 3S shall ,then be tted to the sheathed portion A22' of the structural member directly beneath the extrusion nozzle 23, whereby the whole sheathing between the said clamping means 37, 38 and Ithe leading end of the structural member will safely adhere to the structural member 22, the .action of vacuum never having ceased. The tail end vof the sheathedrmember can be then trimmed-olf.

It will be understood that this invention is not limited to the Vembodiment shown on the drawing. More particularly, the clamping means 27, 28 and 37, 38 have been illustrated .in one of their lsimplest forms in association with an L-shaped structural member. With more elaborate structural members, such .as the one shown in FIGURE 2, two lor more spongy rubber blocks orf suitable configuration or .even other clamping means equivalent to the ones shown, will be employed, which are all referred to in the appended claims by the general term vof clamping means. Further moditications are possible without departing from the scope of the .appended claims.

What I claim is: Y

1. In a process of sheathing with synthetic thermoplastic material an elongated structural member having a concave angle in its .cross-sectional outer profile by extruding on the member a sheath of the material in a softened condition While advancing the structural member longitudinally through an extrusion orifice, the improvement which comprises, clamping .the thermoplastic material radially inwardly in the direction of said angle circumferentially of -said member valong a narrow, circumteren-tial zone immediately adjacent the leading end of the structural member when it passes out of said orice to form a fluid-tight seal between .the material land said member throughout said zone, advancing the structural member through said orifice to sheath the structural member circumferentially and longitudinally while maintaining said huid-tight seal in said zone, providing a short passageway through said zone to provide communication through said uid-tight zone underneath said material .along said concave angle, applying a vacuum. at the leading end of said member to said passageway while .advancing said member through said extrusion orifice to exhaust air longitudinally of said member along said concave angle while clamping the material along said zone, and setting the thermoplastic material while applying said vacuum and maintaining said zone clamped.

2. In a process of sheathing with synthetic thermoplastic material an elongated structural member having a concave angle in its cross-sectional outer prole byextruding on the member a sheath ofthe material in a softened condition while advancing the structural member longitudinally through an extrusionorlitice, the improvement which comprises, clamping the thermoplastic material radially inwardly in the direction of said: angle and circumferentially of said member along a narrow circumferential zone immediately adjacent the leading end of the structural member when it passes out of said orice `to form a fluid-tight seal between the material and said member throughout said zone, advancing the structural member through said orifice to sheath lthe structural member circumferentially and longitudinally while maintaining said Huid-tight seal in 'said zone, prior to clamping said material yalong said narrow zone providing a short passageway through said zone to provide communication through said fluid-.tight zone underneath said material along said concave angle, applying a vacuum at the leading end of said member to said passageway while advancing :said member through said extrusion orifice, to exhaust air longitudinally of said member along said concave angle while cl-amping the material along said Zone, .and setting the thermoplastic material ,while applying vsaid vacuum and advancing said member through said orce, clamping radially inwardly said material in the `direction of said angle and circumferentially of said member along another narrow zone substantially adjacent the trailing end of said structural member to form a Huid-tight seal between the material in said other zone and said member, and continuing to clamp said material at both of said zones while applying said vacuum and setting the material.

3. In la process of sheathing with synthetic thermoplastic material an elongated structural member having a concave angle in its cross-.sectional outer profile by .extruding on the member `a sheath of the material n a softened condition while advancing the structural member longitudinally through `an extrusion orifice in an eX- trusion head to which a vacuum is applied in operation, the improvement which comprises, clamping the thermoplastic material radially inwardly in the direction of said angle land circumferentially of the member -along -a narrow Zone ladjacent the leading end of the structural member when it passes out of said orifice to form a fluidtight seal between the material and said member throughout said zone, advancing the structural member through said orifice to sheath the structural member .circumferentially `and longitudinally while maintaining said uidtight seal in said zone, prior to clamping said material circumferentially along said narrow zone providing a short passageway through said zone to provide communication through said `huid-tight zone underneath said material along said concave angle, applying a supplemental vacuum at the leading end of said member to said passageway while advancing said member through said extrusion orifice to exhaust air longitudinally of said member along Isaid concave `angle while clamping .the material along said zone, .and setting the thermoplastic material while lclamping said zone and applying said supplemental vacuum :and advancing said member through said orifice.

4. In a process of sheathing with synthetic thermoplastic material an elongated structural member having a concave angle in its cross-sectional outer profile by extruding on the member a sheath of the material in la softened condition while advancing the structural member longitudinally .through an extrusion ori-ce in an extrusion head to which `a vacuum is applied in operation, the improvement which comprises, clamping the thermoplastic material radially inwardly in the direction of said `angle and circumferentially of said member along =a narrow zone at the leading end of the structural member when it passes out of said orifice to form a fluid-tight seal between the material and said member throughout said zone, advancing the structural member through said orifice to sheath .the structural member circumferentially and longitudinally while maintaining said duid-tight seal in said zone, prior to clamping of said material circumferentially `along said narrow zone providing la short passageway through said zone to provide communication through said fluid-tight zone underneath said material along said concave angle, applying a supplemental vacuum at the leading end of said member to said passageway -while advancing said member through said extrusion orifice to exhaust air longitudinally of said member along said concave angle while clamping the material along said zone, and setting the thermoplastic material while applying said supplemental vacuum and advancing said member through said orifice, clamping the thermoplastic material radially inwardly in the direction of said angle .and circumferenti-ally lof said member along `another narrow zone adjacent the trailing end of said structural member to -form a fluid-tight seal between the material in said zone and said member, and continuing to clamp the material at both of said zones while applying said supplemental vacuum yand setting the material.

5. In an apparatus for sheathing with synthetic thermoplastic material an elongated structural member having ya concave angle in its cross-sectional outer profile by extruding on the member a sheath :of the material in a softened `condition while advancing the structural member longitudinally through an extrusion orifice, Ithe improvement which comprises, means for clamping the thermoplastic material radially inwardly in the direction of -said angle Iand circumferentially of said member along a narrow circumferential zone .at the leading end of lthe structural member when it passes out lof said orifice to form a fluid-tight seal between the material and said member throughout said Zone, while advancing the structural member through said orice to sheath the structural rmember circumferentially :and longitudinally, a needle insertable under said sheath through said zone prior to clamping said material for providing `a short passageway through said zone underneath said material along said concave angle, means for applying a vacuum at Ithe leading end of said member to said needle providing said passageway while advancing said member through said extrusion orifice to exhaust air longitudinally of said member along said concave angle while clamping said material at and setting the thermoplastic material, and stretchable band means for contracting radially inwardly in the direction of said angle and circumferentially of said member the material yalong another zone adjacent the trailing end of said member to form a fluid-tight seal along said other zone to permit application of a vacuum longitudinally of said member with a sheath thereon.

References Cited in the file of this patent UNITED STATES PATENTS 1,419,090 Williams June 6, 1922 2,145,941 Maxeld Feb. 7, 1939 2,276,004 Vidal et al. Mar. 10, 1942 2,392,707 Taylor Jan. 8, 1946 2,601,243 Botts et al. June 24, 1952 2,736,897 Parsons Feb. 28, 1956 2,956,305 Raydt et al. Oct. 18, 1960 FOREIGN PATENTS 453,123 Great Britain Sept. l, 1936 205,145 Australia Jan. 4, 1957 

1. IN A PROCESS OF SHEATING WITH SYNTHERIC THERMOPLASTIC MATERIAL AN ELONGATED STRUCTURAL MEMBER HAVING A CONCAVE ANGLE IN ITS CROSS-SECTIONAL OUTER PROFILE BY EXTRUDING ON THE MEMBER A SHEATH OF THE MATERIAL IN A SOFTENED CONDITION WHILE ADVANCING THE STRUCTURAL MEMBER LONGITUDINALLY THROUGH AN EXTRUSION ORIFICE, THE IMPROVEMENT WHICH COMPRISES, CLAMPING THE THERMOPLASTIC MATERIAL RADIALLY INWARDLY IN THE DIRECTION OF SAID ANGLE CIRCUMFERENTIALLY OF SAID MEMBER ALONG A NARROW, CIRCUMFERENTIAL ZONE IMMEDIATELY ADJACENT THE LEADING END OF THE STRUCTURAL MEMBER WHEN IT PASSES OUT OF SAID ORIFICE TO FORM A FLUID-TIGHT SEAL BETWEEN THE MATERIAL AND SAID MEMBER THROUGHOUT SAID ZONE, ADVANCING THE STRUCTURAL MEMBER THROUGH SAID ORIFICE TO SHEATH THE STRUCTURAL MEMBER CIRCUMFERENTIALLY AND LONGITUDINALLY WHILE MAINTAINING SAID FLUID-TIGHT SEAL IN SAID ZONE, PROVIDING A SHORT PASSAGEWAY THROUGH SAID ZONE TO PROVIDE COMMUNICATION THROUGH SAID FLUID-TIGHT ZONE UNDERNEATH SAID MATERIAL ALONG SAID CONCAVE ANGLE, APPLYING A VACUUM AT THE LEADING END OF SAID MEMBER TO SAID PASSAGEWAY WHILE ADVANCING SAID MEMBER THROUGH SAID EXTRUSION ORFICE TO EXHAUST AIR LONGITUDINALLY OF SAID MEMBER ALONG SAID CONCAVE ANGLE WHILE CLAMPING THE MATERIAL ALONG SAID ZONE, AND SETTING THE THERMOPLASTIC MATERIAL WHILE APPLYING SAID VACUUM AND MAINTAINING SAID ZOND CLAMPED. 